Variations in fibre composition of the gastrocnemius muscle in rats subjected to speed training

Abstract

Thirty-six adult Wistar rats were divided into three groups. One group was used as a control, and the other two underwent different training programmes in which greater relevance was attached to the intensity of exercise than to its duration. Samples of the red and mixed portions of m. gastrocnemius (caputlateralis) were stained with m-ATPase to determine the percentage of type 1, IIA and IIB fibres, and with NADH-TR in order to quantify variations in the percentage of low staining intensity (FG) fibres. The most notable results obtained were: a) the ratio of type 1 type 11 fibres remained unchanged; b) the proportion of IIA fibres increased, while that of IIB fibres decreased correspondingly; c) FG fibres, which were virtually absent from the red portion, recorded a clear decrease which was more marked, and occurred more rapidly, than in IIB fibres. These differences were al1 statistically significant in the mixed portion of the muscle. Adaptative changes in fibre composition in the red portion were less marked.